The present invention relates to an apparatus for the analysis of elements by inductive plasma spectrometry produced by air. It more particularly applies to the analysis of elements, such as beryllium, which may be contained in air and more generally to the analysis of elements likely to be present in aerosols, liquids, or gases.
"analysis" is understood to means a detection possibly accompanied by dosing and the element can be a solid (e.g. solid particles contained in air), a liquid or a gas (e.g. carbon dioxide gas in the air).
An apparatus for the analysis of elements by plasma spectrometry is already known. This apparatus, which is diagrammatically shown in FIG. 1, comprises a tube 2 made from a refractory material, an exciting source, constituted by an induction coil 4 surrounding a central portion of the tube and energized by a high frequency generator 6, a double injection system 8 permitting the injection of argon as the plasmagenic gas, as well as the central injection of a liquid solution (or vapours of a solution) containing the element to be analysed and a spectrophotometer 10 permitting the analysis of the light emitted by the plasma formed in the tube, in the central portion thereof, and the measurement of the intensity of a characteristic emission line of the element to be analysed, said measurement representing the concentration of said element in the solution.
The light emitted by the plasma is collected by a lens 12, which focuses said light onto the entrance of the spectrophotometer and the latter is connected to a measuring means such as a galvanometer 14, which makes it possible to measure said intensity.
The tube 2 is open at one end and closed at its other end. As can be seen in FIG. 2, an intermediate tube 16, coaxial to tube 2, extends within the latter between said closed end and coil 4. The intermediate tube 16, whose diameter is obviously smaller than that of tube 2, has an open end and another closed end coinciding with the closed end of tube 2.
An injection tube 18, whose diameter is smaller than that of the intermediate tube 16 traverses, parallel to the axis of tube 2 and in a tight manner, the closed end of intermediate tube 16 and ends substantially level with the open end of tube 16.
The injection means 8 compromise a compressed argon cylinder 20, which communicates in tight manner, via a valve 23 and in the vicinity of the closed end of tube 2, with the space between said tube 2 and the intermediate tube 16.
With a view to the injection of the solution, the injection means 8 also comprise injection tube 18, a chamber 22 connected to the end of tube 18, which is not located within tube 2, an atomizer 24 controlled by a not shown ultrasonic generator and communicating with said chamber 22, said atomizer serving to contain the solution to be injected, a compressed argon cylinder 26 communicating on the one hand with the atomizer 24 and on the other with the chamber 22, by means of a member 28 making it possible to pass argon from cylinder 26 to chamber 22 and to atomizer 24.
When the ultrasonic generator is operating and the argon from cylinder 26 reaches chamber 22, small droplets of solution, formed by the ultrasonics in the atomizer 24 and which reach the chamber 22, are entrained by the argon into injection tube 18.
A plasma 30 containing the element to be analysed is then formed, as a result of the argon coming from cylinder 20, in that portion of tube 2 surrounded by the turns of coil 4. The light emitted by the plasma is analysed by the spectrophotometer 10.
Thus, the operation of the known apparatus, diagrammatically shown in FIG. 1, requires the injection of argon as the plasmagenic gas for forming and maintaining the plasma, as well as the injection of the solution to be analysed into the central channel of the plasma torch, said central channel being the injection tube 8 and the torch comprising the tubes 2, 16 and 18.
The apparatus shown in FIG. 1 suffers from the disadvantage of not permitting the direct analysis of an element, such as beryllium, liable to be contained in air. Thus, for analysing the beryllium contained in air, it is firstly necessary to trap said beryllium on a filter and produce a solution from the beryllium trapped on the filter, so that the analysis of the beryllium is carried out a posteriori through the apparatus shown in FIG. 1.